1. Field of the Invention
The present invention relates to a multilayer electronic component including a balun.
2. Description of the Related Art
One of electronic components for use in transmission/reception circuits of wireless communication apparatuses such as cellular phones and wireless LAN communication apparatuses is a balun for converting between an unbalanced signal and a balanced signal. It is required of the balun to exhibit a good amplitude balance characteristic and a good phase balance characteristic over a wide frequency band. The good amplitude balance characteristic means that two balanced element signals that constitute a balanced signal output from the balun have an amplitude difference of approximately zero. The good phase balance characteristic means that the two balanced element signals have a phase difference of approximately 180 degrees.
Marchand baluns, such as ones disclosed in JP 2004-056799A and JP 2006-270444A, are known as wideband capable baluns.
Mobile communication systems conforming to the Long Term Evolution (LTE) standard have become practically used in recent years, and further, practical use of mobile communication systems conforming to the LTE-Advanced standard, which is an evolution of the LTE standard, is under study. Carrier Aggregation (CA) is one of the key technologies of the LTE-Advanced standard. CA uses multiple carriers called component carriers simultaneously to enable wideband transmission.
A mobile communication apparatus operable under CA uses multiple frequency bands simultaneously. Accordingly, such a mobile communication apparatus requires a balun operable in a wider band than was previously possible.
Further, it is particularly required of mobile communication apparatuses that the electronic components such as baluns for use therein be reduced in size.
JP 2004-056799A discloses a technique to achieve an increased bandwidth of a balun by connecting two Marchand baluns in parallel to form a single balun. One of the two Marchand baluns is composed of a first coupling line and a second coupling line, and the other is composed of a third coupling line and a fourth coupling line. JP 2004-056799A also discloses a technique to achieve a further increase in bandwidth of the balun by using a multiwire coupling line to form each of the first to fourth coupling lines. The multiwire coupling line is composed of at least one first line and second lines, one each second line being located on either side of each first line.
However, the balun disclosed in JP 2004-056799A has the following problems. More specifically, in the balun disclosed in JP 2004-056799A, all the first to fourth coupling lines are located on the same surface of a semiconductor substrate. The balun thus occupies a large area and is difficult to miniaturize. Further, attempting to miniaturize the balun would bring a plurality of lines that should not be coupled to each other into close proximity to each other to generate unwanted coupling between those lines, thus resulting in failure to provide desired characteristics.